IEM Daily Feature
Friday, 01 September 2017

Precipitable Water

Posted: 01 Sep 2017 05:34 AM

This week the daily features have been looking at precipitation climatologies for Iowa. In general, there is a northwest to southeast pattern with intensities increasing the further south you travel. One of the reasons for this gradient is the featured map for today. It shows a climatology from one of the main weather forecast models in this country for a variable known as preciptable water. This term is simply the depth of liquid water in the atmosphere above our heads if all of the water was condensed. The amount of water in the atmosphere is important to consider when looking at rainfall rates. The water coming as rain has to come from somewhere. So while the differences shown on this plot may not look large, on average a storm in southern Iowa will have about 10% more water (primarily water vapor) to work with than a storm over northern Iowa. These difference add up over the course of a year and help explain the differences in amount of rain. The observant reader may wonder why then there is not a more NW to SE gradient? Generally, that is likely more to do with the common storm track paths, which is a proxy to jet stream orientation.

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Tags:   preciptablewater